Research On Realistic Rendering Of Translucent Materials And Its Applications In Virtual Reality

Most materials in the real world are translucent,including human skin,foodstuffs,minerals,wood products and chemical products such as soaps and cosmetics.The soft appearance of translucent materials is dependent on the transmission of light within the medium,in addition to the interaction of light on the surface.Perceptual research has shown that there is a strong link between the human perception of the material properties of translucent objects,the shape of the surface and the direction of light.In order to render translucent materials realistically,this dissertation investigates the physical principles of their generation,their graphical implementation and the corresponding perceptual evaluation,and applies the results to the rendering of tumour appearance in virtual surgery.First,the representation of translucency in graphics is investigated.The subsurface scattering that causes translucency is commonly approximated in the field of rendering by means of a bipolar model.Based on an analysis of the factors associated with the estimation of the bipolar model,a method for representing translucency using a local orthogonal coordinate system is proposed.The method takes into account the normal vector of the local region of the surface,the tangential vector,the distance vector from the incident point to the exit point and the optical properties of the object material.Experiments are carried out using this local orthogonal coordinate system to render translucent materials with high scattering and high absorption,and the differences in the appearance of the resulting translucency under different light directions are analyzed,providing a reference for sampling bipolar class models for adjustable and controllable rendering of translucent materials.Secondly,a method for generating highlights for translucent materials based on surface reflection is proposed.The method is easy to integrate with the commonly used bi-directional surface reflection function(BRDF)based highlight generation model,and is able to achieve realistic rendering results by adding highlighting effects with complete preservation of surface details.It also maintains the original level of translucency to avoid a metallic-like appearance.The resulting look improves the perception of object translucency by reducing the contrast in colour intensity while maintaining localized areas of peak colour intensity.A model for the generation of highlight effects based on directed subsurface scattering is then proposed.The model relies on the direction of the incident light as it enters the interior of the medium and the direction as it exits the medium,making the highlight effect directly related to subsurface scattering.The chosen shadow mask function,as opposed to the shadow mask function of the Smith model,generates highlights with a larger number of pixels and larger average intensity values over a wider range of angular illumination directions,provided that the maximum value of the generated highlight intensity is the same.The result is a rendering that retains the shape of the edge and area textures while more closely resembling the image obtained by adding Ground Truth highlights via the path tracing method.Finally,the rendering of translucent materials was applied to the rendering of a glioma in a virtual surgical simulation of brain surgery.For the rendering of the brain glioma,a tissue-based parametric approach was used,using a directed dipole model.Gliomas with a realistic appearance were rendered by configuring biological tissue optical parameters to the directed bipolar model.Further rendering of a realistic glioma model reconstructed from MRI images was achieved by adding multiple surface scattering effects based on microfacets,microslopes to generate the model,obtaining the appearance of enhanced surface very fine edges and maintaining the translucency and transmissivity of the surrounding areas,enabling the rendering of a highly realistic patient glioma model,providing a powerful visual representation for surgical simulation.This dissertation investigates elements related to realistic rendering of translucent materials,including translucency representation,surface reflection-based and subsurface scattering-based appearance simulation,and fine-scale detail enhancement of translucent materials incorporating microfaceted meta-scale multiple scattering effects.The goal of realistic rendering of translucent materials is initially achieved through rich rendering results and graphical and perceptual evaluation.